Skin cleansing compositions routinely include abrasive particles for cleansing the skin (e.g., removal of dirt, sebum, or oil) or improving the appearance of the skin (e.g., exfoliation). Abrasive particles are commonly made from petroleum-based synthetic polymers like polystyrene, cross-linked styrene (XST), polyurethane (PU), polyolefins or waxes. Unfortunately, these petroleum-based synthetic polymers may present long-term disposal problems and potentially have adverse effects on the environment.
On the other hand, natural abrasives such as abrasives derived from plants, shells such as from nuts, or mineral materials, may present poor aesthetics. They may also be too abrasive for use on facial skin. Thus some abrasive particles for use in a skin cleansing composition tend to be overly abrasive and can damage the skin, especially when applied on more sensitive facial skin surfaces.
Recently, biobased polymers like polyhydroxy alkonates (PHA) have attracted significant attention because they are made from renewable plant resources. These materials can be recycled using biological processes (i.e., biorenewable or biodegradable) to reduce greenhouse gas emission and conserve resources.
Features such as size, texture and shape of the abrasive particles also play an important role in the consumer acceptance of skin cleansing compositions. In many cases the visibility of larger abrasive particles signals exfoliation benefits of the product to consumers. Larger abrasive particles also tend to have better tactile properties in use. Visible particles also distinguish particular products in the market place and to identify products having particular beneficial cleaning properties via abrasive particles. Larger sized particles however, that are more visable, tend to be less abrasive and may yield poor or inadequate cleansing and exfoliation performance as evidenced by lack of removal of skin cells, soil or make-up, which may remain on the skin after use.
Furthermore, cleansing compositions with smaller particles may feel more gritty or may be overly abrasive. Consumers selecting a facial cleanser may avoid compositions that feel gritty or overly coarse. Thus formulators often must balance between smaller particles which may be overly abrasive and coarse potentially causing damage on the skin surface, and larger, gentler abrasive particles with a better tactile feel and that are more visable in the product but with reduced or inadqueate exfoliation efficacy.
Therefore, improved skin cleansing compositions that comprise biodegradable abrasive particles with adequate skin cleansing and exfoliating benefits and good tactile properties are needed. Providing a skin cleansing composition with the right balance of these particle properties provides multiple consumer benefits. These improved compositions are more biodegradable, have visible larger particles that have desired tactile properties and have adequate exfoliation efficacy from a distribution of smaller particles with larger surface area.